Combine the egg whites, cornstarch, salt, sherry, baking powder and baking soda in a medium bowl and stir to combine. Pour over chicken in a sealable plastic bag and refrigerate for at least 30 minutes. Remove the chicken pieces from the bag, shake off the excess liquid, and give them another roll in some cornstarch.

Heat about a teaspoon of vegetable oil over medium-high heat in a large saucepan or wok. Saute the ginger and garlic for 30 seconds, then add all remaining ingredients, except for the green onions. Bring the sauce to a boil. Decrease the heat to low and simmer for 15 minutes, stirring occasionally. Set aside.

Next prepare the chicken (or tofu if using). If you prefer a thicker coating, remove the chicken pieces from the baggie and roll them in some extra cornstarch. Heat some vegetable or peanut oil on high in a wok, deep fryer, or heavy skillet and carefully lower the chicken into the oil. Fry until crispy golden brown on all sides. Using a slotted spoon, transfer the chicken pieces to paper towels to absorb the oil.

Add the chicken pieces (or prepared tofu) and green onions to the sauce, stir to coat, and bring the sauce to a low simmer and cook for 5 minutes. Serve immediately with steamed rice and fresh orange slices (optional).